A porous ceramic honeycomb structure has been broadly used as exhaust gas purification means or the like, and as a method of manufacturing the porous ceramic honeycomb structure, a method is performed in which a formed structure is prepared using a ceramic material to which a binder, a pore former or the like has been added, and the formed structure is dried and fired. In this case, it is general to raise the temperature at a constant speed in a firing atmosphere in a firing step. As the binder, organic binders such as methyl cellulose and hydroxypropyl methyl cellulose are used, because formability is satisfactory. Furthermore, as the pore former, various pore formers are used for purposes. A pore former which burns at low temperature, such as starch, has an advantage that it is burnt out in an early stage of the firing step. Therefore, a manufacturing method in which the firing atmosphere is switched to an inert gas from atmospheric air in an early stage at low firing atmosphere temperature has been frequently used because the formed structure needs to be fired in an inert gas atmosphere as in the method of manufacturing a ceramic structure formed of SiC or the like. Even in a manufacturing method in which the formed structure is fired in the atmospheric air as in a method of manufacturing a ceramic structure formed of cordierite or the like, a pore former which burns at a low temperature, such as starch, is used together with a pore former which burns at a high temperature, such as carbon, in order to increase porosity.
Additionally, in recent years, the enhancement of the porosity has advanced from demands for reduction of pressure loss, enhancement of collection efficiency or the like, and a porosity of 40% or more has been a mainstream in the porous ceramic honeycomb structure for use as exhaust gas purification means. Therefore, an addition amount of the pore former, for example, starch or the like tends to increase year by year. In recent years, it has been a mainstream that the ceramic material contains about 20% by mass of the pore former.
However, the addition of a large amount of pore former causes a new problem in the conventional method of manufacturing the porous ceramic honeycomb structure, that is, a problem that cracks are generated in an obtained ceramic structure for an unknown cause, when the formed structure containing a large amount of pore former for obtaining the high porosity is fired in a temperature raising program similar to a conventional program. This has been a large trouble in manufacturing a ceramic structure having high porosity.
The present invention has been developed in consideration of the above-described problem, and an object thereof is to provide a method of manufacturing a porous ceramic structure, which is capable of manufacturing ceramic structures having not only a low porosity but also a high porosity without generating any crack during the firing.